This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. My project aims at determining the oxygen diffusion capacity within cell spheroids ranging from 4000 cells to 100,000 cells with a diameter of the order 100 microns to 1000 microns respectively. Currently I am working with a standard confocal microscope which appears to penetrate to a maximum depth of 100 microns into my sample. With the use of the MPM I am hoping to get a deeper penetration into my sample which will give me a better understanding of the behavior of cells within in the center of the spheroid and their response to hypoxia.